The present invention relates to a process for converting crude semichlorinated copper phthalocyanine or crude partially sulfonated semichlorinated copper phthalocyanine into a highly transparent pigment of high tinctorial strength.
In the past crude copper phthalocyanine has been converted to pigmentary grade material by solvent milling as disclosed in U.S. Pat. Nos. 2,799,594 and 2,799,595 or by acid pasting as disclosed in 3,024,247. The products produced in this manner do not exhibit high transparency, and encapsulation in polymers, such as disclosed in U.S. Pat. No. 3,806,464, has been used to improve transparency. The process of the present invention involves an acid treatment of a preground semichlorinated copper phthalocyanine pigment, which is lower in cost than either acid pasting or solvent milling and produces highly transparent products without the complication of added polymeric resins.
The effect of contact with sulfuric acid solutions of various concentrations on the crystal phase of copper phthalocyanine and monochloro copper phthalocyanine has been described by B. Honigmann et al Zeitschrift fur Kristallographic 122, pp 185-205 (1965) and B. Honigmann, Berichte der Bundesgesellschaft, 71 (1967).